1. Field of the Invention
The invention relates generally to an apparatus for testing geological and other naturally occuring and fabricated samples to determine their mechanical properties. The invention particularly relates to an apparatus for conducting constant-strain-rate triaxial tests. The apparatus is designed so that the confining pressure/axial stress ratio remains constant.
2. Description of the Prior Art
A testing apparatus is known wherein a self-supporting sample is subjected to external forces in a tri-axial cell. The term sample is used to describe both geological samples and other naturally occuring and fabricated articles. A tri-axial cell typically comprises a pressure chamber, in which the sample can be located, a means for applying a force to the sample, and a means for measuring the force applied to the sample. With such an apparatus various characteristics of the sample under test, such as its compressive and shear strengths, can be determined.
U.S. Pat. No. 3,505,860, Bishop, et. al, discloses a geological sample testing apparatus having a cylinder containing the sample, and a piston and a hydraulic fluid as means for applying forces to the sample. In utilizing the apparatus in Bishop, two forces are applied to the cylinder having the sample disposed therein. The first force is applied to the hydraulic fluid through the base of the cylinder and is coupled to apply force to the axial axes of the sample. The second force is applied mechanically via the piston to the longitudinal axis of the sample. The axial movement of the piston, under various loads, correlates to the structural properties of the sample.